Photocurable acrylic coating composition

ABSTRACT

A photocured acrylic coat comprised of the photoreaction products of: 
     (i) at least one photocurable polyfunctional acrylate monomer; 
     (ii) at least one phenyl ketone photoinitiator; and 
     (iii) at least one active ultraviolet radiation absorber selected from benzotriazoles, cyanoacrylates, and hydroxybenzophenones. The coating is substantially completely or completely cured and provides improved protection to the substrate against ultraviolet radiation. The coating is also nonopaque or transparent.

This is a divisional of co-pending application Ser. No. 944,031 filed on12/22/86 now abandoned.

BACKGROUND OF THE INVENTION

Aromatic carbonate resins are well known thermoplastic resins which, dueto their many excellent mechanical properties, are used as thermoplasticengineering materials. The aromatic carbonate resins exhibit, forexample, optical clarity, good thermal stability, good impactproperties, and toughness. These resins are utilized as films, sheetarticles, and molded articles.

However, the aromatic carbonate resins are somewhat susceptible tosurface scratching and abrasion, attack by many common solvents, and todegradation by ultraviolet radiation. The problems of relatively lowscratch and abrasion resistance and susceptibility to attack by chemicalsolvents have been addressed by providing various surface coatings onaromatic carbonate resin articles which coatings serve to protect theunderlying substrate from scratching and attack by chemical solvents.Among the various coatings used to protect the aromatic carbonate resinarticles are the acrylics Some of these acrylic coatings are describedin U.S. Pat. Nos. 3,968,305, 3,968,309, and 3,582,398.

Certain acrylic coatings have been found to be particularly advantageouswhen applied onto aromatic carbonate resin articles. These coatings maygenerally be characterized as the ultraviolet radiation cured, i.e.,photocured, acrylic coatings. U.S. Pat. No. 4,198,465 describes apolycarbonate article having on its surface a UV cured acrylic coatingcomprised of the photoreaction products of (i) at least onepolyfunctional acrylate monomer having from 2 to about 4 functionalgroups attached to an aliphatic hydrocarbon residue containing 1-20carbon atoms and optionally having ether linkages and/or hydroxylgroups, (ii) a photoinitiator, and (iii) resorcinol monobenzoate; U.S.Pat. No. 4,384,026 describes an aromatic carbonate resin article havingon its surface an ultraviolet radiation cured coating comprised of thephotoreaction products of polyfunctional acrylate monomers and acrylicmodified polymers; and U.S. Pat. No. 4,477,529 describes a plasticarticle having adhered thereto a translucent and decorative ultravioletradiation cured coating which is wrinkled in a macroscopically irregularbut microscopically regular manner and comprised of the photoreactionproducts of (i) at least one polyfunctional acrylate monomer, (ii)certain polysiloxane-polyether block copolymer surfactants, and (iii)azobisisobutyronitrile.

In order to protect the underlying aromatic carbonate resin substratefrom degradation by ultraviolet radiation the acrylic coatings maycontain ultraviolet radiation absorbers or stabilizers. Theseultraviolet radiation absorbers may be latent ultraviolet radiationabsorbers such as, for example, resorcinol monobenzoate described in theaforediscussed U.S. Pat. Nos. 4,198,465 and 4,477,529, or activeultraviolet radiation absorbers such as those described inaforediscussed U.S. Pat. No. 4,384,026. The incorporation of ultravioletradiation absorbers, particularly the active absorbers, intophotocurable acrylic coating compositions, however, presents somewhat ofa problem since these coating compositions must also contain aphotoinitiator or photosensitizer in order to effect the cure of thepolyfunctional acrylate monomers. Generally, the presence of the activeultraviolet radiation absorbers in the photocurable coating compositionsresults in an incomplete cure of the coating composition. This is due tothe fact that these active absorbers absorb ultraviolet radiationthereby reducing the amount of said radiation available to activate thephotoinitiators. This reduces the effectiveness of the photoinitiatorsthereby resulting in an incomplete cure of the polyfunctional acrylatemonomers. The incomplete cure of the coating composition results in acoating having reduced weathering resistance as compared with acompletely cured coating.

While this problem of incomplete cure is generally not significant withthe use of latent ultraviolet radiation absorbers such as resorcinolmonobenzoate, these latent absorbers are generally not quite aseffective as the active absorbers. Thus, while the coatings containingthese latent absorbers are quite useful for most applications therenevertheless exist certain applications where coatings exhibiting betterprotection against ultraviolet radiation are required.

It is, therefore, an object of the instant invention to provide aromaticcarbonate resin articles having adhered to at least one surface thereofa photocured acrylic coating containing an active ultraviolet radiationabsorber wherein said coating is substantially completely or completelycured and exhibits improved weatherability.

SUMMARY OF THE INVENTION

The instant invention is directed to an aromatic carbonate resin articlecoated with a photocured acrylic coating containing an activeultraviolet radiation absorber, said coating being substantiallycompletely or completely cured and exhibiting improved weatherability.More particularly, this coating is obtained by the photocure of aphotocurable coating composition comprised of (i) at least onephotocurable polyfunctional acrylate monomer, (ii) a particularphotoinitiator or photosensitizer selected from certain phenyl ketones,and (iii) an active ultraviolet radiation absorber or stabilizerselected from benzotriazoles, hydroxybenzophenone, cyanoacrylates, ormixtures thereof.

DESCRIPTION OF THE INVENTION

It has been surprisingly discovered that by the use of a combination ofcertain specific photoinitiators and certain active ultravioletradiation absorbers photocured acrylic coatings containing active UVabsorbers can be provided which are completely cured and which exhibitimproved weatherability. The presently available photocured coatingscontaining an active ultraviolet radiation absorber are generallyincompletely cured and, therefore, exhibit reduced weatherability. Thecoatings of the instant invention exhibit substantially the same degreeof weatherability as those photocured acrylic coatings containing alatent ultraviolet radiation absorber while at the same time affordingimproved protection against ultraviolet radiation to the underlyingaromatic carbonate substrate.

The instant photocured coatings are obtained by the photocure of aphotocurable coating composition comprised of: (i) at least onephotocurable polyfunctional acrylate monomer, (ii) at least oneparticular photoinitiator selected from certain phenyl ketones, and(iii) an active ultraviolet radiation absorber selected frombenzotriazoles, hydroxybenzophenones, cyanocarylates, or mixturesthereof.

While these coatings may be applied onto a variety of plastic substratessuch as acrylics, polyphenylene ethers, aromatic carbonate resins, andthe like, they are particularly useful on aromatic carbonate resinsubstrates.

The aromatic carbonate resins include both the high molecular weightthermoplastic polycarbonate resins and the copolyester-carbonate resins.Both types of resins are described hereinafter.

The polycarbonate resins utilized in the instant invention areconventional well-known resins which are generally commerciallyavailable or may be readily prepared by well-known conventional methods.These polycarbonates, as well as methods for their preparation, aredescribed inter alia in U.S. Pat. Nos. 3,161,615, 3,220,973, 3,312,659,3,312,660, 3,313,777, 3,666,614, and 3,939,672, all of which areincorporated herein by reference. The polycarbonate resins may beconveniently prepared by the interfacial polymerization process by thecoreaction of at least one dihydric phenol with a carbonate precursor.Typically, the dihydric phenols utilized may be represented by thegeneral formula ##STR1## wherein:

R is independently selected from halogen, monovalent hydrocarbon, andmonovalent hydrocarbonoxy radicals;

R¹ is independently selected from halogen, monovalent hydrocarbon, andmonovalent hydrocarbonoxy radicals;

W is selected from divalent hydrocarbon radicals, --S--, --S--S--,--O--, ##STR2##

n and n¹ are independently selected from integers having a value of from0 to 4 inclusive; and

b is either zero or one.

The monovalent hydrocarbon radicals represented by R and R¹ include thealkyl, cycloalkyl, aryl, aralkyl and alkaryl radicals. The preferredalkyl radicals are those containing from 1 to about 12 carbon atoms. Thepreferred cycloalkyl radicals contain from 4 to about 8 ring carbonatoms. The preferred aryl radicals contain from 6 to 12 ring carbonatoms, i.e., phenyl, biphenyl, and naphthyl. The preferred aralkyl andalkaryl radicals contain from 7 to about 14 carbon atoms.

The preferred halogen radicals represented by R and R¹ are chlorine andbromine.

The divalent hydrocarbon radicals represented by W include the alkylene,alkylidene, cycloalkylene and cycloalkylidene radicals. The preferredalkylene radicals are those containing from 2 to about 30 carbon atoms.The preferred alkylidene radicals are those containing from 1 to about30 carbon atoms. The preferred cycloalkylene and cycloalkylideneradicals are those that contain from 6 to about 16 ring carbon atoms.

The monovalent hydrocarbonoxy radicals represented by R and R¹ may berepresented by the formula --OR² wherein R² is a monovalent hydrocarbonradical of the type described hereinafore. Preferred monovalenthydrocarbonoxy radicals are the alkoxy and aryloxy radicals.

Some illustrative non-limiting examples of dihydric phenols of Formula Iinclude:

2,2-bis(4-hydroxyphenyl)propane (bisphenol-A);2,2-bis(3,5-dibromo-4-hydroxyphenyl)propane;2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane;1,1-bis(4-hydroxyphenyl)cyclohexane;1,1-bis(3,5-dimethyl-4-hydroxyphenyl)cyclohexane;1,1-bis(4-hydroxyphenyl)decane; 1,4-bis(4-hdroxyphenyl)propane;1,1-bis(4-hydroxyphenyl)cyclododecane;1,1-bis(3,5-dimethyl-4-hydroxyphenyl)cyclododecane; 4,4'-thiodiphenol;and bis(4-hydroxyphenyl)ether.

Other dihydric phenols which are useful are described in U.S. Pat. Nos.2,998,835, 3,028,365, and 3,334,154, all of which are incorporatedherein by reference.

The carbonate precursor may be a carbonyl halide; a carbonate ester, ora bishaloformate. The carbonyl halides may be carbonyl bromide, carbonylchloride, or mixtures thereof. The carbonate esters may be diphenylcarbonate; di(halophenyl)carbonates such as di(bromophenyl) carbonate,di(chlorophenyl)carbonate, and di(tribromophenyl)carbonate;di(alkylphenyl) carbonates such as di(tolyl)carbonate; di(naphthyl)carbonate, chlorophenyl chloronapthyl carbonate; and phenyltolyl carbonate. The bishaloformates that can be used include thebishaloformates of dihydric phenols such as the bischloroformates ofbisphenol-A and hydroquinone; and the bishaloformates of glycols such asthe bischloroformates of ethylene glycol, neopentyl glycol, andpolyethylene glycol. The preferred carbonate precursor is carbonylchloride, also known as phosgene.

A convenient process for the preparation of the instant polycarbonatesis the interfacial polymerization process. The interfacialpolymerization process utilizes two different solvent media which areimmiscible. One solvent medium is an aqueous basic medium. The othersolvent medium is an organic medium, such as methylene chloride, whichis immiscible in said aqueous medium. Also employed in the interfacialpolymerization process are molecular weight regulators which control thechain length or molecular weight of the carbonate polymer by a chainterminating mechanism, and catalysts. The molecular weight regulatorsare well known in the art and include, but are not limited to, phenolitself, p-tertiarybutyl phenol, and chroman I. The catalysts are alsowell known in the att and include, but are not limited to, tertiaryamines such as triethylamine, quaternary ammonium compounds such astetraethylammonium bromide, and quaternary phosphonium compounds such asn-butyltriphenyl phosphonium.

Also included within the term polycarbonates are the randomly branchedthermoplastic polycarbonates wherein a branching agent, which isgenerally a polyfunctional aromatic compound, is reacted with thedihydric phenol and the carbonate precursor. These polyfunctionalaromatic compounds contain at least three functional groups which may becarboxyl, hydroxyl, carboxylic anhydride, haloformyl, and mixturesthereof. Some illustrative non-limiting examples of these aromaticpolyfunctional compounds include trimellitic anhydride, trimelliticacid, trimellityl trichloride, 4-chloroformyl phthalic anhydride,pyromellitic acid, pyromellitic dianhydride, mellitic acid, melliticanhydride, trimesic acid, and benzophenonetetracarboxylic acid.

The aromatic copolyester-carbonate resins are likewise well known in theart and are described, along with methods for their preparation, interalia, in U.S. Pat. No. 3,169,121, incorporated herein by reference.Briefly stated, the copolyester carbonates comprise recurring carbonategroups, carboxylate groups, and aromatic carbocyclic groups in thelinear polymer chain in which at least some of the carbonate groups andat least some of the carboxylate groups are bonded directly to ringcarbon atoms of the aromatic carbocyclic groups.

These copolyester-carbonates contain ester bonds and carbonate bonds inthe polymer chain, wherein the amount of ester bonds is from about 25 toabout 90 mole percent, preferably from about 35 to about 80 molepercent. For example, 5 moles of bisphenol-A reacting completely with 4moles of isophthaloyl dichloride and one mole of phosgene would give acopolyester-carbonate of 80 mole percent ester bonds.

The copolyester-carbonates may conveniently be prepared via theinterfacial polymerization process by reacting at least one dihydricphenol, a carbonate precursor, and at least one ester precursor. Theester precursor may be a difunctional carboxylic acid or preferably areactive ester forming derivative of said difunctional carboxylic acid.Some illustrative non-limiting examples of difunctional carboxylic acidsinclude isophthalic acid and terephthalic acid. Some illustrativenon-limiting examples of the reactive ester forming derivatives of thedifunctional carboxylic acids are isophthaloyl dichloride andterephthaloyl dichloride.

The active UV absorber containing acrylic coating which is disposed onat least one surface of the aromatic carbonate resin article is obtainedby photocuring a photocurable coating composition comprised of (i) atleast one polyfunctional acrylate monomer, (ii) a photoinitiatorselected from certain acetophenones, and (iii) at least one active UVabsorber selected from benzotriazoles, hydroxybenzophenones, andcyanolacrylates. The coating is prepared by applying the coatingcomposition onto the surface of the aromatic carbonate resin article,and then exposing the coating composition to UV radiation of sufficientintensity and for a period of time effective to form said cured coating.

The polyfunctional acrylate monomers which comprise the major portion ofthe coating composition may be represented by the general formula##STR3## wherein:

R³ is either the methyl radical or hydrogen;

c is an integer having a value of from 2 up to the number of replaceablehydrogen atoms present on R², preferably from 2 to about 8, morepreferably from 2 to about 6, and most preferably from 2 to 4; and

R² is a c functional hydrocarbon residue, a c functional substitutedhydrocarbon residue, a c functional hydrocarbon residue containing atleast one ether linkage, or a substituted c functional hydrocarbonresidue containing at least one ether linkage.

The preferred monomers of Formula II are those wherein R³ is hydrogen.

The c functional hydrocarbon residues represented by R² include thealiphatic, preferably the saturated aliphatic, hydrocarbon residues, thealiphatic-aromatic hydrocarbon residues, and the aromatic hydrocarbonresidues.

Preferred c functional hydrocarbon residues are the c functionalaliphatic, preferably saturated, hydrocarbon residues containing from 1to about 20 carbon atoms, the c functional aliphatic-aromatichydrocarbon residues containing from 7 to about 20 carbon atoms, and thec functional aromatic hydrocarbon residues containing from 6 to about 14carbon atoms.

Preferred c valent hydrocarbon residues containing at least one etherlinkage are the c valent aliphatic hydrocarbon residues, preferablysaturated aliphatic hydrocarbon residues, containing from 1 to about 5ether linkages and from 2 to about 20 carbon atoms.

Preferred c valent substituted hydrocarbon residues are the c valentaliphatic hydrocarbon residues, preferably the saturated aliphatichydrocarbon residues, containing from 1 to about 20 carbon atoms, the cvalent aliphatic-aromatic hydrocarbon residues containing from 7 toabout 20 carbon atoms, and the c valent aromatic hydrocarbon residuescontaining from 6 to 14 carbon atoms, which contain substituent groups.The number of substituent groups may vary but is preferably from 1 toabout 4 substituent groups. The preferred substituent groups areselected from hydroxyl, halogens, amino, nitro, --COOH, and --COOR'wherein R' is an alkyl group of 1 to about 6 carbon atoms or an arylgroup of from 6 to 12 ring carbon atoms. The substituent groups may bethe same or different if more than one substituent group is present.

Preferred c valent substituted hydrocarbon residues containing at leastone ether linkage are the c valent aliphatic hydrocarbon residues,preferably the saturated aliphatic hydrocarbon residues, containing from2 to about 20 carbon atoms and from 1 to about 5 ether linkages, whichcontain substituent groups. The number of substituent groups may varybut is preferably from 1 to about 4 substituent groups. The preferredsubstituent groups are selected from hydroxyl, halogens, amino, nitro,--COOH and --COOR' wherein R' is as defined hereinafore. The substituentgroups may be the same or different when more than one substituent groupis present.

The more preferred polyfunctional acrylic monomers of Formula II arethose wherein R³ is hydrogen and R² is selected from c functionalsaturated aliphatic hydrocarbon residues containing from 1 to about 20carbon atoms, hydroxyl substituted c functional saturated aliphatichydrocarbon residues containing from 1 to about 20 carbon atoms, cfunctional saturated aliphatic hydrocarbon residues containing from 2 toabout 20 carbon atoms and from 1 to about 5 ether linkages, and hydroxylsubstituted c functional aliphatic saturated hydrocarbon residuescontaining from 2 to about 20 carbon atoms and from 1 to about 5 etherlinkages.

When c is 2 in Formula II the c functional acrylates are thediacrylates. When c is 3 in Formula II the c functional acrylates arethe triacrylates. When c is 4 in Formula II the c functional acrylatesare the tetraacrylates.

Some illustrative non-limiting examples of saturated aliphaticdiacrylates and dimethacrylates include: ##STR4##

Some illustrative non-limiting examples of saturated aliphaticdiacrylates containing at least one ether linkage include: ##STR5##

Some illustrative non-limiting examples of aromatic diacrylates include##STR6##

Some illustrative non-limiting examples of saturated aliphatictriacrylates and trimethacrylates include: ##STR7##

Some illustrative non-limiting examples of aromatic triacrylates andtrimethacrylates include ##STR8##

Some illustrative non-limiting examples of saturated aliphatic andaromatic tetraacrylates and tetramethacrylates include: ##STR9##

The polyacrylates and polymethacrylates and their preparation are wellknown in the art. Indeed, many of the polyfunctional acrylates andmethacrylates are commercially available or may be prepared by wellknown and conventional methods. One of the methods of producing the di-,tri- and tetraacrylate esters involves reacting acrylic acid ormethacrylic acid with a di-, tri- to tetrahydroxyl containing compoundto produce the diester, triester, or tetraester. Thus, for example,acrylic acid can be reacted with ethylene glycol to produce ethyleneglycol diacrylate.

Although the coating compositions of the instant invention may containonly one of said polyfunctional acrylate or methacrylate monomers,preferred coating compositions contain a mixture of two or moredifferent polyfunctional monomers, preferably a diacrylate and atriacrylate. When the coating compositions contain a mixture of acrylatemonomers it is preferred that the ratio, by weight, of the diacrylate ordimethacrylate to a higher functional monomer such as the triacrylate befrom 30:70 to about 70:30. Exemplary mixtures of diacrylates andtriacrylates include mixtures of hexanediol diacrylate withpentaerithritol triacrylate, hexanediol diacrylate withtrimethylolpropane triacrylate, diethyleneglycol diacrylate withpentaerythritol triacrylate, and diethyleneglycol diacrylate withtrimethylolpropane triacrylate.

While the corresponding coatings may likewise contain the polymerizedphotoreaction products of a single polyfunctional acrylate ormethacrylate monomer, coatings containing the polymerized photoreactionproducts of two different polyfunctional acrylate or or methacrylatemonomers, preferably a diacrylate and a triacrylate.

Generally, the coating composition contains from about 70 to about 95weight percent of said polyfunctional acrylate monomers. The UV curedmethacrylate monomers, preferably a diacrylate and a triacrylate.

Generally, the coating composition contains from about 70 to about 95weight percent of said polyfunctional acrylate monomers. The UV curedcoating contains from about 70 to about 95 weight percent of thephotocured reaction products of said polyfunctional acrylate monomers.

The phenyl ketone photoinitiator or photosensitizer of the instantinvention may be represented by the general formula: ##STR10## wherein:

R⁵ is independently selected from halogen, hydroxy, monovalenthydrocarbon, substituted monovalent hydrocarbon, monovalenthydrocarbonoxy, or substituted monovalent hydrocarbonoxy radicals;

R⁴ is selected from monovalent hydrocarbon radicals, substitutedmonovalent hydrocarbon radicals, monovalent hydrocarbon radicalscontaining at least one ether linkage, or substituted monovalenthydrocarbon radicals containing at least one ether linkage:

and d is an integer having a value of from 0 to 5 inclusive.

The monovalent hydrocarbon radicals represented by R⁴ and R⁵ areprefereably those containing from 1 to about 20 carbon atoms. Theyinclude the alkyl, aryl, aralkyl, alkaryl, and cycloalkyl radicals. Thepreferred alkyl radicals are those containing from 1 to about 20 carbonatoms. They may be straight chain or branched alkyl radicals. Thepreferred cycloalkyl radicals are those containing from about 4 to about8 ring carbon atoms. The preferred aralkyl and alkaryl radicals arethose containing from 7 to about 20 carbon atoms. The preferred arylradicals are those containing from 6 to 12 ring carbons, i.e., phenyl,naphthyl, and biphenyl.

The substituted monovalent hydrocarbon radicals are those monovalenthydrocarbon radicals described above which contain substituent groupsthereon, preferably from 1 to about 4 substituent groups. The preferredsubstituent groups are the halogens, preferably chlorine and bromine,and hydroxyl groups. When more than one substituent group is presentthey may be the same or different.

The monovalent hydrocarbonoxy radicals represented by R⁵ may berepresented by the formula --OR⁶ wherein R⁶ is a monovalent hydrocarbonradical of the type described hereinafore.

The substituted monovalent hydrocarbonoxy radicals represented by R⁵ maybe represented by the formula --OR^(6') wherein R^(6') is a substitutedmonovalent hydrocarbon radical of the type described hereinafore.

The monovalent hydrocarbon radicals containing at least one etherlinkage represented by R⁴ generally have the formula --R'--R"--_(f)O--R⁷ wherein R' and R" are independently selected from divalenthydrocarbon radicals, R⁷ is a monovalent hydrocarbon radical of the typedescribed hereinafore, and f has a value of from 0 to about 20.

The divalent hydrocarbon radicals represented by R' and R" arepreferably those containing from 1 to about 20 carbon atoms. Theyinclude the alkylene, cycloclakylene, arylene, alkarylene, andaralkylene radicals. The preferred alkylene radicals, which may beeither straight chain or branched alkylene radicals, are thosecontaining from 1 to about 20 carbon atoms. The preferred cycloalkyleneradicals are those containing from 4 to about 8 ring carbon atoms. Thepreferred aralkylene and alkarylene radicals are those containing from 7to about 20 carbon atoms. The preferred arylene radicals are thosecontaining from 6 to 12 ring carbon atoms, i.e, phenylene, naphthalene,and biphenylene. The preferred divalent hydrocarbon radicals are thealkylene radicals.

It is to be understood that the divalent hydrocarbon radicalsrepresented by R' and R", as well as the monovalent hydrocarbonrepresented by R⁷, may contain substituent groups thereon, preferablyfrom 1 to about 4 substituent groups, which may be the same or differentif more than one substituent group is present. The preferred substituentgroups are the halogens, preferably chlorine and bromine, and hydroxylgroups. When these substituent groups are present on the monovalenthydrocarbon radicals containing at least one ether linkage such radicalsare the substituted monovalent hydrocarbon radicals containing at leastone ether linkage.

Preferred phenyl ketones of Formula III are those wherein R⁵ is amonovalent hydrocarbon radical, preferably an alkyl, or a monovalenthydrocarbonoxy radical, preferably an alkoxy radical, and R⁴ is amonovalent hydrocarbon radical , preferably an alkyl radical, or asubstituted monovalent hydrocarbonoxy radical, preferably a substitutedalkyl radical.

The phenyl ketones of Formula III are well known compounds which aregenerally commercially available or may be readily prepared by wellknown and conventional methods.

Some illustrative non-limiting examples of these phenyl ketones include:

p-phenoxy-2,2-dichloroacetophenone; p-methoxy-2,2-dichloroacetophenone;2-hydroxy-2,2-dimethylacetophenone; 2-hydroxy-2,2-diethylacetophenone;2-hydroxy-2,2-dipropylacetophenone;p-isopropyl-2-hydroxy-2,2-dimethylacetophenone;p-isopropyl-2-hydroxy-2,2-diethylacetophenone;p-n-butyl-2-hydroxy-2-methyl-2-ethylacetophenone;p-dodecyl-2-hydroxy-2,2-dimethylacetophenone;p-phenoxy-2,2-dibromoacetophenone; 2,2-dibromoacetophenone;2,2-dichloroacetophenone; 2,2-dimethylacetophenone;2-hydroxy-2,2-cyclohexylacetophenone;p-cyclohexyl-2,2-dibutylacetophenone;2-2,dimethoxy-2-phenylacetophenone; and 1-hydroxycyclohexane phenylketone.

The amount of the phenyl ketone photosensitizer present in the coatingcomposition is a photosensitizing or photoinitiating amount. Byphotosensitizing or photoinitiating amount is meant an amount effectiveto effect the photocure of the polyfunctional acrylate monomers to thepolymeric cross-linked state. Generally, this amount is from about 0.05to about 10 weight percent, preferably from about 0.1 to about 5 weightpercent. Weight percent of photoinitiator is based on the total amountsof polyfunctional acrylate monomers and photoinitiator present in thecoating composition.

The coating composition also contains an active ultraviolet radiationabsorber or stabilizer selected from the benzotriazoles, cyanoacrylates,hydroxybenzophenones, or mixtures thereof. These ultraviolet radiationabsorbers are active rather than latent absorbers. That is to say theyabsorb ultraviolet radiation from the start rather than being convertedinto active UV absorbers upon exposure to ultraviolet radiation as isthe case with resorcinol monobenzoate.

These ultraviolet radiation absorbers are well known in the art and aregenerally commercially available or may be readily prepared by known andconventional methods. These ultraviolet radiation absorbers are amplydescribed in the literature. The benzotriazole and hydroxybenzophenoneultraviolet radiation absorbers are described in U.S. Pat. Nos.3,309,220, 3,049,443, 3,043,709, 2,976,259, and 4,410,594, all of whichare incorporated herein by reference.

Some illustrative non-limiting examples of the benzotriazoles andhydroxybenzophenones include:

2,2'-dihdroxybenzophenone; 2,2',4,4'-tetrahydroxybenzophenone;2,2'-dihydroxy-4,4'-dimethoxybenzophenone;2,2'-dihydroxy-4,4'-diethoxybenzophenone;2,2'-dihydroxy-4,4'-dipropoxybenzophenone;2,2'-dihydroxy-4-methoxy-4'-ethoxybenzophenone;2,2'-dihydroxy-4-methoxy-4'-propxybenzophenone;2,3'-dihydroxy-4,4'-dimethoxybenzophenone;2,3'-dihydroxy-4-methoxy-4'-butoxybenzophenone;2-hydroxy-4,4',5'-trimethoxybenzophenone;2-hydroxy-4,4',6,-tributoxybenzophenone;2-hydroxy-4-butoxy-4',5'-dimethoxybenzophenone;2-hydroxy-4-ethoxy-2',4'-dibutylbenzophenone;2-hydroxy-4-propoxy-4',6'-dichlorobenzophenone;2-hydroxy-4-propoxy-4',6'-dibromobenzophenone;2,4-dihydroxybenzophenone; 2-hydroxy-4-methoxybenzophenone;2-hydroxy-4-ethoxybenzophenone;2-hydroxy-4-methoxy-4'-methylbenzophenone;2-hydroxy-4-methoxy-4'-ethylbenzophenone;2-hydroxy-4-methoxy-4'-chlorobenzophenone;2-hydroxy-4,4'-dimethoxybenzophenone;2-hydroxy-4,4'-dimethoxy-3-methylbenzophenone;2-hydroxy-4,4'-dimethoxy-2'-ethylbenzophenone;2-hydroxy-4-ethoxy-4'-methylbenzophenone;2-hydroxy-4-ethoxy-4'-methoxybenzophenone;2-hydroxy-4,4'-diethoxybenzophenone;2-hydroxy-4-ethoxy-4'-propoxybenzophenone;2-hydroxy-4-ethoxy-4'-chlorobenzophenone;2-hydroxy-4-ethoxy-4'-bromobenzophenone;2-(2'-hydroxy-5'-methylphenyl)benzotriazole;2-(2'-hydroxy-5'-tert-butylphenyl)benzotriazole;2-(2'-hydroxy-3'-methyl-5'-tert-butylphenyl)benzotriazole;2-(2'-hydroxy-5'-cyclohexylphenyl)benzotriazole;2-(2'-hydroxy-3',5'-dimethylphenyl)benzotriazole;2-(2'-hydroxy-5'-tert-butylphenyl)-5-chlorobenzotriazole; and2-(2'-hydroxy-3'-di-tert-butylphenyl)benzotriazole

Among the cyanoacrylates useful as ultraviolet radiation stabilizers arethose represented by the general formula ##STR11## wherein:

R⁹ is an alkyl, cycloalkyl, hydroxyalkyl, or hydroxycycloalkyl;

⁸ is independently selected from monovalent hydrocarbon radicals,halogen radicals, hydroxy radicals, or monovalenthydrocarbonoxyradicals; and

e is independently selected from integers having a value of from 0 to 5inclusive

The monovalent hydrocarbon radicals represented by R⁸ are those asdescribed for R⁴ hereinafore. The monovalent hydrocarbonoxy radicalsrepresented by R⁸ are those having the formula --OR¹⁰ wherein R¹⁰ is amonovalent hydrocarbon radical of the type described hereinafore. Thepreferred hydrocarbonoxy radicals are the alkoxy radicals.

Preferred alkyl radicals represented by R⁹ are those containing from 1to about 10 carbon atoms. Preferred cycloalkyl radicals are thosecontaining from about 4 to about 8 ring carbon atoms. Preferredhydroxyalkyl radicals are those containing one hydroxyl group and from 1to about 10 carbon atoms. Preferred hydroxycycloalkyl radicals are thosecontaining one hydroxyl radical bonded to a ring carbon atoms of a C₄-C₈ cycloalkyl.

Preferred compounds of Formula IV are those wherein e is zero. Thecyanoacrylates useful in the practice of this invention are described,inter alia, in U.S. Pat. No. 4,129,667, incorporated herein byreference.

The amount of the active ultraviolet radiation stabilizers present inthe instant coating composition is an effective amount, i.e., an amounteffective to protect the underlying aromatic carbonate resin fromdegradation by ultraviolet radiation. Generally, this effective amountis an amount sufficient so that the absorbance of the coating at λmaximum is at least one, which corresponds to absorption at λ maximum ofat least 90% of the incident ultraviolet radiation by the cured coating.The absorbance is calculated using the relationship A=log(I_(o) /I)wherein A is the absorbance, I_(o) is the intensity of incident light,and I is the intensity of transmitted light. Generally, this amount isfrom about 3 to about 15 weight percent, preferably from about 4 toabout 12 percent, and more preferably from about 5 to about 10 weightpercent. Weight percent of ultraviolet radiation absorber is based onthe total amounts of polyfunctional acrylate, photoinitiator, and the UVradiation stabilizer present.

One of the advantages of the instant invention is that relatively largeamounts of UV stabilizer can be present in the coating compositionwithout deleteriously affecting the cure of the composition. Withconventional coating compositions if relatively large amounts of UVabsorber, i.e,, above about 5 weight percent, are present in the coatingcompositions the photocuring of these compositions containing theselarge amounts of active UV absorbers is seriously impared.

It is to be understood that only one UV absorber can be present ormixtures of two or more different UV absorbers of the instant inventionmay be utilized.

In the practice of the instant invention the photocurable coatingcompositions are first prepared by mixing together the polyfunctionalacrylate monomer or monomers, the photoinitiator, and the activeultraviolet radiation absorber. Additionally, if so desired to reducethe viscosity of the coating formulation an organic solvent such asalcohol may optionally be incorporated into the coating formulation.This solvent should preferably one which is non-aggresive towards thearomatic carbonate resin and which evaporates readily. The variouscomponents are thoroughly mixed together so as to form a generallyhomogeneous coating composition. A thin, uniform layer of this coatingcomposition is then applied onto at least one surface of the substrateby any of the known means such as spraying, dipping, painting, or rollcoating. The coating composition is then cured, preferably in an inertatmosphere such as nitrogen, by exposure to ultraviolet radiation whichcan have a wavelength of from 1849 A. to 4000 A. The lamp system used togenerate such radiation can consist of ultraviolet lamps of thedischarge type, for example xenon, metallic halide, metallic arc such ashigh or low pressure mercury vapor discharge lamps, etc., havingoperating pressures from as low as a few millitorr up to about 10atmospheres.

The coating should be thick enough to at least provide protectionagainst surface scratching or abrasion, attack by chemical solvents, andthe deleterious affects of ultraviolet radiation. Generally, thisminimum thickness is at least about 0.05 mil. The maximum thickness ofthe coating is not critical but is controlled by secondaryconsiderations such as appearance, cost, rate of cure of the coatingcomposition, and the like. Generally, a thickness of less than about 3mils is preferred.

The photocured coating compositions of the instant invention are thuscomprised of the (i) cured reaction products of at least onepolyfunctional acrylate monomer, and (ii) at least one active UVabsorber selected from benzotriazoles, cyanoacrylates, andhydroxybenzophenones. The cured coating will, of course, also containthe acetophenone photoinitiator which was present in the coatingcomposition.

The coating compositions of the instant invention, as well as the curedcoatings, may also optionally contain any of the well known and commonlyused additives such as, for example, fillers; surface active agents;antioxidants: and the like. A particularly useful surface active agentor surfactant is a silicone surfactant. The silicone surfactants arewell known in the art and are generally commercially available. They mayinclude the silcione fluids such as the polysiloxane fluids,particularly the diorganopolysiloxane fluids. However, the preferredsilicone surfactants for use in the present invention are thepolysiloxane-polyether block copolymer surfactants. The preferredpolysiloxane-polyether block copolymers are represented by the generalformula ##STR12## wherein:

R¹⁰ is independently a monovalent hydrocarbon radical;

R¹² is a monovalent hydrocarbon radical;

R¹¹ is a lower alkyl radical;

x has a value of at least two, for example from 2 to about 40 or more;

y has a value of 2 or 3;

z has a value of from 2 to 4 inclusive; and

m has a value of at least 5, for examples from 5 to 100.

Among the radicals represented by and R¹⁰ and R¹² are alkyl, cycloalkyl,aryl, aralkyl and alkaryl radicals. The preferred alkyl radicals arethose containing from 1 to about 20 carbon atoms. The preferredcycloalkyl radicals are those containing from about 4 to about 8 ringcarbon atoms. The preferred aralkyl and alkaryl radicals are thosecontaining from 7 to about 14 carbon atoms. The preferred aryl radicalsare those containing from 6 to 12 ring carbon atoms, i.e., phenyl,naphthyl, and biphenyl. The monovalent hydrocarbon radicals representedby and R¹⁰ and R¹² may also contain substituent groups thereon,preferably from 1 to about 3 halogen radicals.

The preferred lower alkyl radicals represented by R¹² are thosecontaining from 1 to about 5 carbons.

In a preferred embodiment of the instant invention both R¹⁰ and R¹² arealkyl or aryl radicals with methyl and phenyl being preferred.

The preparation of these polysiloxane-polyether block copolymers isdescribed in U.S. Pat. Nos. 3,182,076 and 3,629,156, incorporated hereinby reference.

These surfactants may be present in the coating composition in amountsof from about 0.05 to about 3 weight percent, based on the weight of thepolyfunctional acrylate monomer.

PREFERRED EMBODIMENT OF THE INVENTION

In order to more fully and clearly illustrate the present invention thefollowing specific examples are presented. It is intended that theexamples be considered as illustrative rather than limiting theinvention disclosed and claimed herein. In the examples all parts andpercentages are parts and percentages by weight unless otherwisespecified.

The following examples illustrate the present invention.

EXAMPLE 1

A coating composition is prepared by mixing together 50 parts by weightof trimethylolpropanetriacrylate, 50 parts by weight ofhexanedioldiacrylate, 5 parts by weight of2-(2'-hydroxy-5'-t-octylphenyl)benzotriazole, 5 parts by weight of2-hydroxy-2,2-dimethylacetophenone, and 0.5 parts by weight ofsurfactant.

The resulting coating composition is applied onto a polycarbonate testpanel with a no. 6 wire wound bar. The coated panel is then passedthrough a nitrogen blanketed UV curing processor containing two mediumpressure mercury lamps at a conveyor speed of 50 ft/min. The curedcoating is hard, tack free, and abrasion and solvent resistant. Thecoated and cured polycarbonate test panels are exposed to acceleratedweathering in a UVCON apparatus. In this accelerated weathering testsamples are inserted into an accelerated weathering device sold by theAtlas Electric Devices Company. This device is set to alternatingconsecutive cycles of fluorescent ultraviolet light at 70° C. for 8hours and high humidity at 50° C. for 4 hours. The test samples areexposed to this accelerated weathering for 1,000 hours. At the end ofthis period the adhesion of the coating to the polycarbonate substrateis still excellent and the increase in Yellowness Index (as measured inaccordance with ASTM D1925) was 3.9 units.

EXAMPLE 2

The procedure of Example 1 is substantially repeated except that the 5parts by weight of the 2-hydroxy-2,2-dimethylacetophenone photoinitiatorare replaced with 5 parts by weight of 1-hydroxycyclohexylphenyl ketone.The cured coating is hard, tack-free, and abrasion and solventresistant. After 1,000 hours of accelerated weathering the adhesion ofthe coating to the polycarbonate substrate is still good and theincrease in Yellowness Index was 3.5 units.

What is claimed is:
 1. An ultraviolet radiation curable coatingcomposition consisting essentially of:(i) at least one polyfunctionalacrylate monomer; (ii) at least one active ultraviolet radiationabsorber selected from the group consisting of benzotriazoles,cyanoacrylates, and hydroxybenzophenones and mixtures thereof, saidultraviolet radiation absorber being present at a level of from about 5to about 10 weight percent based on the total weight of polyfunctionalacrylate monomers, photoinitiators and UV radiation absorber present inthe composition; and (iii) a photoinitiator selected from the groupconsisting of 2-hydroxy-2,2-dimethylacetophenone, 1-hydroxy cyclohexanephenyl ketone, and 2,2-dimethoxy-2-phenylacetophenone, saidphotoinitiator being present at a level of from about 0.05 to about 10weight percent based on the total weight of the polyfunctional acrylatemonomer and photoinitiator present in the coating composition.
 2. Thecomposition of claim 1 which contains from about 0.1 to about 5 weightpercent of said photoinitiator.
 3. The composition of claim 1 whereinsaid ultraviolet radiation absorber is a benzotriazole.
 4. Thecomposition of claim 1 wherein said polyfunctional acrylate monomer iscomprised of at least one diacrylate monomer and at least onetriacrylate monomer.
 5. An ultraviolet radiation curable coatingcomposition consisting essentially of:(i) at least one polyfunctionalacrylate monomer; (ii) at least one active ultraviolet radiationabsorber selected from the group consisting of benzotriazoles,cyanoacrylates, and hydroxybenzophenones and mixtures thereof, saidultraviolet radiation absorber being present at a level of from about 5to about 10 weight percent based on the total weight of polyfunctionalacrylate monomers, photoinitiators and UV radiation absorber present inthe composition; and (iii) a photoinitiator, said photoinitiator being2-hydroxy-2,2-dimethylacetophenone, said photoinitiator being present ata level of from about 0.05 to about 10 weight percent based on the totalweight of the polyfunctional acrylate monomer and photoinitiator presentin the coating composition.
 6. An ultraviolet radiation curable coatingcomposition consisting of:(i) at least one polyfunctional acrylatemonomer; (ii) at least one active ultraviolet radiation absorberselected from the group consisting of benzotriazoles, cyanoacrylates,and hydroxybenzophenones and mixtures thereof, said ultravioletradiation absorber being present at a level of from about 5 to about 10weight percent based on the total weight of polyfunctional acrylatemonomers, photoinitiators and Uv radiation absorber present in thecomposition; and (iii) a photoinitiator selected from the groupconsisting of 2-hydroxy-2,2-dimethylacetophenone, 1-hydroxy cyclohexanephenyl ketone, and 2,2-dimethoxy-2-phenylacetophenone, saidphotoinitiator being present at a level of from about 0.05 to about 10weight percent based on the total weight of the polyfunctional acrylatemonomer and photoinitiator present in the coating composition.